The bending of metal tubing for special applications, such as, window frames involves a number of considerations in terms of overall length or dimension, cross-sectional size, and the sequence of bending and cutting operations for different lengths. In the production of different sized frames, especially in high volume production, it is desirable to correlate the speed of advancement of the frame section with the overall intended length of the frame as well as the rate of bending for a given cross-sectional configuration or size while at the same time controlling the pressure applied to the frame as it is being bent. Unless the rate of speed is properly controlled with respect to the frame length, there is a tendency to advance the frame member at unduly slow rate of speed and be very time-consuming in turning out sizable quantities of frame members. On the other hand, if the speed selected is too high, it is very difficult to maintain dimensional accuracy in periodically interrupting the advancement of the frame to perform the bend or cut operation. Thus, it is desirable to be able to run the bender at the maximum possible speed for a given length of frame while permitting reduction or deceleration in the speed as it approaches the stopping point for a bending operation. Further, by virtue of the number of variables and parameters that must be considered in bending each different sized frame it is important to closely control the various parameters and to automatically regulate variations in speed, clamping, bending for each different dimension and shape of tube for utmost efficiency and accuracy in operation. Moreover, there are numerous specialized operations in bending and cutting of materials which require manual intervention without interrupting the computer-controlled operation.
Various automated systems have been devised in the past for controlling tube bending operations. To the best of our knowledge, however, none has been devised which will satisfactorily perform the wide range of steps and impose the necessary control in forming rectangular frames for storm window inserts and particularly in such a way as to control the speed of advancement of the workpiece relative to the length between bends, periodic braking and clamping to perform a bend operation, regulate the pressure applied to the frame during the clamping and bending operations, or to vary the bending and cutting pattern according to the length of frame being formed. For example, U.S. Pat. No. 4,261,145 to M. Brocking discloses a method of forming double-paned windows but is concerned specifically with the formation of a butt joint between the cut ends of the frame and wherein the bending apparatus is placed on an inclined work surface or table and requires the use of a movable stop which determines the point or length at which the frame is bent. U.S. Pat. Nos. 4,161,110 to K. Ritter et al and 4,131,003 to G. B. Foster et al disclose automatically controlled bending for rods or tubes as does U.S. Pat. No. 4,100,780 to F. Sassak which discloses a program-controlled bending apparatus to determine the position of bends via orientation and depth of each bend. Moreover, U.S. Pat. Nos. 3,426,562 to F. Inda, 3,808,856 to B. J. Lance and 3,299,681 to C. F. Hautau disclose various apparatus and systems for determining the position or length between bends and a radius or arc of each bend so as to select the proper bending form for the pipe or tube to be bent. Other representative patents are U.S. Pat. Nos. 4,281,530 to W. G. McElhaney and 3,964,289 to J. C. Williamson, Jr.